The birds and the bees don't celebrate Valentine's Day, of course, but some certainly have bizarre mating rituals.

1. Panda "P0RN" to Boost Mating Efforts at Thai Zoo

A Thai zoo hoped that "panda p*rnography" would spark romance between its two giant pandas, which were married by proxy in an elaborate Chinese-style ceremony, we reported in November 2006.

NGS stock photo by Michael Nichols

Chuang Chuang and Lin Hui had called Thailand's Chiang Mai Zoo home for the past four years. Zoo officials hoped that the warm Thai climate would spark the pandas' hormones and trigger their desire to mate, our contributor Brian Handwerk wrote.

"But the animals, on loan from China for ten years, have yet to start a family. A first mating attempt earlier this year failed to produce offspring, and the pandas have remained platonic pals since then -- prompting officials to launch their unique plan," Handwerk reported.

"They don't know how to mate, so we need to show the male how through videos," project chief Prasertsak Buntrakoonpoontawee told the Reuters news service.

Chuang Chuang, the six-year-old male, was to view films of other mating pandas when scientists judged him to be relaxed and receptive -- perhaps just after a tasty dinner.

"If all goes well, the racy video will be both instructional and inspirational, showing Chuang Chuang the reproductive ropes and causing him to see five-year-old Lin Hui in an entirely different light," our report said.

Did it work?

After panda porn failed to spark amour, Thai zoo authorities turned to artificial insemination in the hope of impregnating their lone female giant panda, the Associated Press reported a few months later.

2. Gorillas Photographed Mating Face-to-Face -- A First

A pair of wild western lowland gorillas in Africa surprised researchers by engaging in face-to-face mating, the Wildlife Conservation Society announced last year.

"Though the behavior had been observed before in mountain gorillas, it had never before been seen in the lowland gorilla subspecies -- and had never before been photographed in the wild," National Geographic News reported.

Photograph by Thomas Breuer/Wildlife Conservation Society

"Perhaps just as surprising, the female in the photographs -- Leah, named after Star W@rs's Princess Leia -- is also the first gorilla seen using a tool in the wild," the report said.

Conservation biologist Thomas Breuer took the mating photographs in 2005.

Scientists never expected to observe such a sight.

"Seeing the similarity between humans and gorillas in this respect is fascinating," Breuer said.

"A new study of the species has shown that both ultraviolet reflectance and fluorescence are key to the animals' successful courtship and mating," wrote Aalok Mehta.

Even more interesting is that these signals are gender specific.

Photograph courtesy of Matthew L.M. Lim and Daiqin Li

"Male jumping spiders reflect UV light using patches of scales on their faces and bodies that are displayed during mating stances. But females, when in the presence of UV light, give off green fluorescent light from their palps, small appendages close to their faces," Mehta reported.

Scientists were led to study the animals because they have eyes particularly sensitive to ultraviolet and green light. The researchers quickly found that spiders showed no interest in members of the opposite sex that were not glowing.

"We conclude that sexual coloration is a crucial prerequisite for courtship," the researchers wrote in the journal Science.

Only one other animal has been known to use fluorescence as a possible courtship signal -- the budgerigar, a type of parrot -- said Daiqin Li, lead investigator of the study, via email. "But the effect merely boosted to a limited degree the brightness of the [bird's] yellow body color, and its behavioral relevance has been questioned."

Li speculated that the behavior may have evolved as a way for the spiders to signal their suitability as mates while minimizing unwanted attraction from predators. But it's still d@ngerous, since many spider predators, such as some birds, can see UV light.

4. Damselfly Mating Game Turns Some Males G@y

Disguises used by female damselflies to avoid unwanted sexual advances can cause males to seek out their own s.e.x, a study suggested in 2005.

Belgian researchers investigated why male damselflies often try to mate with each other. The scientists said the reason could lie with females that adopt a range of appearances to throw potential mates off their scent. "In an evolutionary battle of the sexes, males become attracted to a range of different looks, with some actually preferring a more masculine appearance," wrote National Geographic News contributor James Owen.

NGS photo by W.E. Garrett

The study, published in the journal Biology Letters, said such evolutionary selection pressures could also explain homos*xual behavior seen in males of other animals whose females assume a variety of guises. Such "polymorphic" species are seen in dragonflies, butterflies, hummingbirds, and lizards.

The study team found the s*xual preference of male damselflies was influenced by the company they keep, Owen reported. Males that were housed together before being introduced to females tended to seek out their own gender afterward. But males kept in mixed-s.e.x living quarters later preferred all three female forms when choosing a mate.

"This suggests male damselflies are likely to become attracted to other males only when females are absent or scarce. Yet a minority of males still showed an innate preference for male mates," Owen wrote.

The team's findings were reflected in mating behavior observed in the wild, said study author Hans Van Gossum, an evolutionary biologist at the University of Antwerp, Belgium.

Van Gossum said around 17 percent of males in wild populations appear to favor same-s.e.x pairings, while about one in six males in the lab experiments showed the same tendency despite exposure to females. "This behavior can be considered homos*xual," he said.

5. Video: Wild Shark Mating Caught on Camera

Biting, shoving, and wrestling make for rough coupling among nurse sharks. Get a rare eye on the action via a shark-mounted camera.

Video by Wildlife Conservation Society and "Wild Chronicles," airing on PBS, made possible by National Geographic Mission Programs and World Wildlife Fund and presented by WLIW New York